1. Field of the Invention
The present invention relates to the supply of integrated circuits and, more specifically, to the integration of one or several voltage regulators with the supplied circuit. The present invention more specifically relates to linear D.C./D.C. regulators. Such regulators essentially comprise one control stage and one or several power stages.
2. Discussion of the Related Art
FIG. 1 partially and schematically shows a linear regulator of the type to which the present invention applies.
A power stage 1 comprises one or several MOS transistors 2 having one power terminal 3 (drain or source) connected to a D.C. supply voltage Vps and having its other power terminal 4 (source or drain) providing regulated voltage Vdd. Gate or control terminal 5 of power transistor 2 is connected to the output of a control stage 10 of the regulator. This control stage essentially comprises a comparator 11 (COMP) of a voltage representative of regulated output voltage Vdd with a reference voltage Vref. This reference voltage is most often provided by a commonly-called “bandgap” circuit 12. In the shown example, the voltage representative of the regulated output voltage is obtained by means of a resistive dividing bridge formed of two resistors R1 and R2 in series between terminal 4 and ground GND. Finally, a capacitor 6 damps the variations of the reference value provided by comparator 11 by connecting gate 5 of transistor 2 to ground GND. Circuit 12 and comparator 11 are generally supplied by voltage Vdd. A same control stage 10 can control several power stages 1 all taking part in the provision of voltage Vdd (block 1 shown in dotted lines in FIG. 1). All these stages then receive the same control signal CTRL from stage 10. Similarly, within a same power stage, all transistors receive the same control signal.
The operating principle of a D.C./D.C. series regulator is perfectly well known in the art. The concept of a power transistor used in the present invention does not refer to a high voltage, but to the fact that the power stage must convey a relatively significant supply current (generally ranging between a few hundreds of microamperes and approximately 1 ampere).
The use of a D.C/D.C. regulator in an integrated circuit is linked to the presence of a supply voltage Vps, provided to the circuit, which is greater than supply voltage Vdd of the internal circuit components.
Regulated voltage Vdd is intended to supply different functions linked to the application specific to the integrated circuit. The circuits executing these functions are generally integrated in what is called the circuit core while the regulator, and more specifically its power stages, may be integrated in what is called the integrated circuit crown.
FIG. 2 shows, in a partial simplified top view, a conventional example of embodiment of an integrated circuit 20. In the example of FIG. 2, core 21 of the integrated circuit integrates the functions linked to the application as well as the control stage(s) (not shown in detail) of the voltage regulators. The power stages of the voltage regulator(s) are, as for themselves, integrated in crown 22 of the integrated circuit. This crown surrounds core 21.
Crown 22 generally includes what is called a supply rail (RING) 23 which comprises two conductors 24 and 25 conveying the respective most positive and most negative supply voltages Vps and GND of the integrated circuit. The supply rail may be only partial at the periphery or be arranged differently in the integrated circuit (for example, at the center). The notion of core encompasses, whatever their position, the integrated elements performing the different functions associated with the application specific to the integrated circuit and supplied by a rail having any shape.
An example of an integrated circuit in which the voltage regulation power stages are arranged in an input/output crown of an integrated circuit chip is described in U.S. patent application Ser. No. 09/886,967, which is incorporated herein by reference. The solution described in this document consists of integrating, in the crown locations intended for the input/output pads of the circuit, the power stages, and more specifically, the power transistors of the regulators. The supply rail is, as for itself, untouched.
According to the type of integrated circuit, the general bulk thereof may be linked either to the number of circuits in the core, or to the number of input/output pads necessary for its external connections.
In the first case, the circuit is said to be of “core limited” type, which means that its size is limited by the surface area of the circuit core and not by the perimeter necessary to align on its edges all the input/output pads. Accordingly, the surface area unused by input/output pads in the crown is used for the core. The forming of the power blocks in the crown accordingly reduces the areas recovered by the core, which results in an increase in the circuit size.
Conversely, when the size of the product is limited by the alignment of the input/output pads and not by the core surface area, it is said to be of “pad limited” type. For a constant number of input/output pads, the forming of the power blocks in the crown accordingly increases its perimeter, and thus the circuit surface area.
Further, the surface area required by the integration of the power stages requires, as described in the above-mentioned US document, the flowing of additional signals which each time transit from the core to the crown.